As shown in FIG. 1, a method using a reflector 2 in a radio communication system is proposed in order to improve communication quality between a radio base station BS and a mobile station UE. The reflector 2 is configured to reflect a radio wave radiated primarily from the radio base station BS (a transmission side apparatus) so that the radio wave is reflected secondarily.
To be more specific, as shown in FIG. 1, the radio wave radiated primarily from the radio base station BS is blocked by an obstacle 4 such as a building. Therefore, the mobile station UE located in a shadow region 3 is unable to ensure a line-of-sight path from the radio base station BS, and thus is unable to ensure a desired communication quality.
To address this, in the radio communication system disclosed in Patent Document 1 described above, the reflector 2 is installed in a position that allows the mobile station UE to ensure a line-of-sight path from the radio base station BS, and the reflector 2 radiates the radio wave reflected off the reflector 2, to the shadow region 3 from behind the obstacle 4. Accordingly, the radio communication system disclosed in the above-described Patent Document 1 can improve the communication quality in the shadow region 3.
In general, a direction in which the radio wave radiated primarily from the radio base station BS and then made incident on the reflector 2 can travel is determined in accordance with a place where the reflector 2 is installed and an angle at which the reflector 2 is installed.
To be more specific, as shown in FIG. 2, the radio wave (an incident wave) made incident on the reflector 2 through a medium 1 (air) having a refractive index n1 is reflected off a surface of the reflector 2 and then travels in a direction at a reflection angle of specular reflection of the radio wave.
Here, the incident angle of the radio wave is defined as “θi1” and the reflection angle of the radio wave is defined as “θr1”. In this case, if the radio wave is made incident as a plane wave, it is known that (Formula 1) holds true by solving a boundary condition with the surface of the reflector defined as a boundary surface.θi1=θr1  (Formula 1)
Specifically, the radio wave (a reflected wave) reflected off the surface (the boundary surface) of the reflector 2 travels in a direction at the angle θr1 (a direction of specular reflection) which is the same as the incident angle θi1 of the radio wave (the incident wave).
That is to say, the above-described radio communication system employs the reflector 2 which is configured to reflect the radio wave radiated primarily from the radio base station BS (the transmission side apparatus) so that the radio wave is radiated secondarily to a desired area.
The above-described radio communication system, however, involves the following problem. Specifically, the radio wave which is radiated primarily from the radio base station BS and then made incident on the reflector 2 can only travel in the direction at the above-mentioned reflection angle of the specular reflection. Hence, in an environment where the angle at which the reflector 2 is installed is not sufficiently adjustable, the radio wave may be unable to be radiated secondarily to the desired area (the shadow region 3).
The present invention has been made in view of the foregoing problem and an object of the present invention is to provide a radio communication system which employs a scatterer configured so that a radio wave radiated primarily from a transmission side apparatus is radiated secondarily by the scatterer in directions other than a direction at a reflection angle of specular reflection.